The synthesis and crystal structure of a new copper(I)
polymer,
[{(Ph3P)2Cu2(μ-Cl)2(μ-pyrazine)}∞],
are reported.
The polymer is photoluminescent with its emission maximum at
16 340 cm-1 at a temperature of 20 K.
The
emitting state is assigned with the assistance of excited state
distortions determined by using resonance Raman
intensities. The polymer consists of
(PPh3)(pyz)Cu(μ-Cl2)Cu(pyz)(PPh3)
units in which pyrazine ligands bridge
copper pairs to form a chain of dimers. The packing arrangement
contains two inversion centers. Each dimer
has an inversion center between the two coppers and the bridging
chlorine atoms. A second inversion center is
located in the center of the pyrazine ligand, which links the dimers in
an infinite linear chain. The nitrogen atom
of the pyrazine, the phosphorus atom of one triphenylphosphine, and the
two chlorine atoms form a slightly
distorted tetrahedron about the copper. The largest distortions in
the lowest excited electronic state, determined
from the resonance Raman intensities, occur along totally symmetric
modes of the pyrazine ligand. The emission
is assigned to copper(I) to pyrazine charge transfer.
The electronic absorption and resonance Raman spectra of the metal diimine dithiolate complexes M(mnt)-(baba) where M = Ni and Pd, mnt = l,Zmaleonitrile, and baba = biacetylbisaniline are reported. The absorption spectra obtained from a low temperature frozen glass exhibit weakly resolved vibronic structure.The spectra are interpreted by using the time-dependent theory of spectroscopy. The electronic spectra are fit by using a calculation method for electron transfer spectra that includes coupling between potential surfaces (including the coupling of electronic and nuclear motions, i.e. the breakdown of the Born-Oppenheimer approximation). The results of this detailed calculation are compared to those involving uncoupled potential surfaces. Quantitative bond length changes are calculated. The distortions on both ligands that are observed support the assignment of the lowest energy excited state as arising from a ligand to ligand electron transfer transition from the dithiolate ligand to the diimine ligand.
The resonance Raman spectra of the metal-to-metal charge transfer (MMCT) mixed-valence complex [(OC) 5 Cr 0 -CN-Os III (NH 3 ) 5 ](CF 3 SO 3 ) 2 are measured and analyzed. The excitation profiles (the Raman intensities as a function of excitation wavelength) are obtained using the SO 3 stretch of the triflate ion as an internal standard. The ratios of the Raman intensities are not constant with different excitation wavelengths. This unusual observation is attributed to interference between two overlapping electronic states of the molecule. The electronic states are observed in the low-temperature polarized single crystal absorption spectrum. The resonance Raman intensities and excitation profiles are calculated with the time dependent theory of spectroscopy and include the interference between the electronic states. The origin of the unusual intensities is quantitatively explained in terms of the real and imaginary parts of the Raman cross sections from the two states.
Resonance Raman spectra, a normal coordinate analysis, and
calculation of excited-state bond lengths and angles
of
bis[hydrotris(3,5-dimethyl-1-pyrazolyl)borato]copper(II)
are reported. Raman spectra are obtained in resonance
with a ligand field state and the lowest ligand-to-metal charge
transfer (LMCT) excited state. A normal coordinate
analysis is carried out using Raman and IR frequencies and resonance
Raman intensities to assist in the assignment
of the symmetric modes. Potential energy distributions (PED) and
force constants are reported. The individual
bond length changes are calculated by using the resonance Raman
intensities and the PED. Bond length and
angle changes throughout the entire three-dimensional skeleton are
reported. The signs of the bond length changes
in the pyrazolyl borate ring are interpreted in conjunction with the
results of a molecular orbital calculation. The
NN bond length decreases by 0.02 Å, the CN bond lengths increase
by 0.05 and 0.08 Å, the Cu−N bond
increases by 0.10 Å and the NBN angle decreases by 2° in the
LMCT excited state.
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